Beyond Pre-Anaesthetic Testing

Nick Carmichael

BVM&S, BSc VetSci(Hons), Diploma VCS(Syd),

Diploma RCPath, Diplomate ECVCP, MRCVS

Aims of pre-anaesthetic testing Screen for the presence of intercurrent

disease Allow adjustments in anaesthetics/ drugs

used to be made Provide baseline data if problem develops

later

Benefits of pre-anaesthetic testing Safer anaesthesia Appropriate perioperative management Early identification of clinically silent

problems

Drawbacks of pre-anaesthetic testing Cost benefit analysis “False positive” screening test results Inappropriate labelling of cases “False negative” screening test results Decision time pressure

Cost Benefit Analysis

Detection rate of abnormalities ~ 1-11% veterinary

Detection rate of abnormalities~ 2% man Evidence of reduced anaesthetic morbidity

and mortality~ ??

What are the major anaesthetic risks? Excessive anaesthetic administered Hypotension Cardiac rhythm abnormalities/ arrest Ventilation/perfusion imbalances

Would pre- anaesthetic bloods predict / ameliorate these?

Pre-anaesthetic testing requirements Sensitive Specific Relate to organ function Low cost

Diagnostic Profiles Contains grouped tests

related to organ function Tests provide

complimentary information

Tests included relate to a presenting sign

Assists in localisation/ narrowing of the DDx

Screens Contains a single test

per organ Single most sensitive

test included Test array is fixed Provides yes/no

information regarding normality

SCREENS VS PROFILES

Pre-anaesthetic screen components FBC Total protein Urea ALT ALP Glucose (Electrolytes)

Full Blood Count abnormalities in Pre-anaesthetic screens

Tiny, boxer male 3yr

Total protein 68 g/L (54.0 -77.0 )

Urea 3.3 mmol/L (2.0 -9.0 )

Creatinine 91 umol/L (40.0 -106.0)

Alk Phos * 707 U/L High (0.0 -150.0 )

ALT * 233 U/L High (0.0 -25.0 )

Total bilirubin 6 umol/L (0.0 -20.0 )

Glucose 5.3 mmol/L (3.5-6.5)

Tiny, boxer male 3yr

RBC * 2.83 x10^12/L Low (5.0 -8.5 ) Hb * 6.9 g/dl Low (12.0 -18.0 ) HCT *21.9 % Low (37.0 -55.0 ) MCV 77.0 fl (60.0 -80.0 ) MCH 24.3 pg (19.0 -26.0 ) MCHC 31.5 g/dl (31.5 -37.0 ) Platelets * 66 x10^9/L Low (160 -500 ) WBC * 1.89 x10^9/L Low (6.0 -15.0 ) Neutrophils * 39% 0.74 x10^9/L Low (3.0 -11.5 ) Lymphocytes 57% 1.08 x10^9/L (1.0 -4.8 ) Monocytes 3% 0.06 x10^9/L (0.0 -1.3 ) Eosinophils 1% 0.02 x10^9/L (0.0 -1.25 )

FBC abnormalities

White Cells : Atypical Lymphocytes

FBC abnormalities

Red Cells: Schistocytes

FBC abnormalities

Platelets: Thrombocytopenia & Platelet Clumps

Daisy, CKCS FN 2yrs

Total protein ↑86 68 g/L Albumin 32 32 g/L Globulin ↑54 36 g/L Total calcium 2.86 2.70 mmol/L Phosphate ↑3.51 2.10 mmol/L Urea ↑14.9 ↑13.3 mmol/L Creatinine 101 ↑152 umol/L Alk Phos ↑578 ↑455 U/L GLDH ↑87 12 U/L Gamma GT 25 25 U/L Total bilirubin ↑30 6 umol/L Bile acids ↑26.7 9.7 umol/L

Glucose 6.4 5.6 mmol/L

Interpretation of Biochemical results

Total Protein

Normal TP 50:50 alb:glob Normal TP, 10:90 AG

Hypoalbuminaemia

SignificanceAnaesthesiaWound healingeffusion formation

CausesIncreased lossReduced productionEffusion formation

Hypoalbuminaemia

Investigation

Evidence of effusion /exudation Evidence of increased renal/ GI loss? Evidence of inflammation? Evidence of impaired hepatic function?

Hyperglobulinaemia

Associated with

Inflammation Viral infection Neoplasia

Severe Hyperglobulinaemia

Effects Impaired primary haemostasis Blood hyperviscosity

Differentials Feline viral infections

FIV, FIP, Felv B-cell derived neoplasia

Lymphoma, myeloma, (plasmacytoma) Non indigenous infections

Leishmania, Ehrlichia, Borrelia

Hyperglobulinaemia

Diagnostic evaluation

Clinical examination FBC – smear evaluation Viral screening Serum protein electrophoresis Non indigenous infection serology/ PCR

testing

Tess 11y, FN Cross breed dogEpistaxis for 1 year, NAD on skull XrayRBC ↓ 3.67 x10^12/L 5 - 8.5Hb ↓ 9.0 g/dl 12 - 18HCT ↓ 27.8 % 37 - 55MCV 76.0 fl 60 - 80MCH 24.5 pg 19 - 26MCHC 32.4 g/dl 31.5 - 37Platelets 357 x10^9/L 160 - 500WBC 8.46 x10^9/L 6 - 15Neutrophils 77% 6.5x10^9/L 3 - 11.5Lymphocytes 20% 1.6x10^9/L 1 - 4.8Monocytes 0.% 0.0x10^9/L 0 - 1.3Eosinophils 3% 0.2x10^9/L 0 - 1.25

Rouleaux

Tess 11y, FN Cross breed dogEpistaxis for 1 year, NAD on skull XrayTotal protein ↑ 138 g/L 54.0 - 77.0 Albumin ↓ 22 g/L 25.0 - 37.0 Globulin ↑ 116 g/L 25.0 - 52.0 A:G ratio ↓ 0.2 0.6 - 1.5 Total calcium 2.60 mmol/L 2.0 - 3.0Corrected Calcium 2.96 mmol/l 2.0 - 3.0 Urea ↑ 9.4 mmol/L 2.0 - 9 Creatinine 97 umol/L 40 - 106 Alk Phos 4 U/L 0 - 150 ALT ↑ 45 U/L 0 - 25 Total bilirubin 7 umol/L 0 - 20 Glucose 5.7 mmol/L 3.5 - 6.5

Diagnostic evaluation of liver disease Useful information

Is there liver disease present likely to be exacerbated by anaesthetic agents?

Is liver function significantly impaired?Metabolising/clearing anaesthetic agentsProduction of coagulation proteins

Diagnostic evaluation of liver diseaseIs liver disease present?

Hepatocellular damageALT

CholestasisALP

Hepatocyte Enzyme Distribution

Hepatic Lobule Anatomy

Cholestatic Enzyme Markers

Hepatocellular ALT: High Low

ALP 1/2 life: 66 hours 6 hours

Steroid induced ALP: Yes No

Bilirubinuria: Normal Abnormal

Cholangiohepatitis: Rare Common

Liver Enzymes in Dogs and Cats

Transaminases & Dehydrogenases

ALT AST GLDH

Measure integrity of cell membranesMeasure integrity of cell membranesDegree of increase correlates with number of Degree of increase correlates with number of hepatocytes involvedhepatocytes involvedAST increases correlate with more severe AST increases correlate with more severe hepatocelullar injuryhepatocelullar injury

Measure integrity of cell membranesMeasure integrity of cell membranesDegree of increase correlates with number of Degree of increase correlates with number of hepatocytes involvedhepatocytes involvedAST increases correlate with more severe AST increases correlate with more severe hepatocelullar injuryhepatocelullar injury

Interpreting liver Enzymes

Increased ALT Primary hepatic disease? Reactive hepatopathy? Induced change?

Derived from muscle?

Interpreting liver Enzymes

Increased ALP Primary cholestatic problem? Reactive hepatopathy? Induced change? Hepatic lipidosis? Canine benign hepatic nodular hyperplasia? Physiological increase?

Interpreting liver Enzymes

Differentiating primary and secondary hepatopathies

Clinical criteriaHistory, physical exam

Presence of hyperbilirubinaemia Extent of increase in ALT Changes in endogenous liver function

indicators OFTEN FURTHER TESTING WILL BE REQUIRED

Liver Function Tests

Endogenous Albumin, urea,

Glucose, Cholesterol, Coagulation Factors, NH3

Endogenous Albumin, urea,

Glucose, Cholesterol, Coagulation Factors, NH3

“Alarm” blood screen abnormalities in liver disease Marked increases in ALT Increased bilirubin Reductions in urea, albumin, A:G ratio,

cholesterol Microcytosis +/- anaemia

Further investigation of liver abnormalities Review history and physical findings Run a liver profile with FBC Include post prandial bile acids Consider abdominal imaging

Liver Function Tests

Darby PandyTotal protein 67 64 g/LAlbumin 33 33 g/LGlobulin 34 31 g/LAG ratio 1.0 1.1 Urea 2.5 4.3 mmol/LCreatinine 76 87 umol/L Alk Phos ↑ 302 865 U/L ALT ↑ 81 46 U/L AST 27 26 U/L GLDH ↑ 12 7 U/L Gamma GT 1 11 U/L Total bilirubin 9 5 umol/LGlucose 5.6 5.8 mmol/LCholesterol 6.5 5.7 mmol/L Bile acids ↑ 162.2 0.9 umol/L Post bile acids ↑ 270.8 20.8 umol/L

Tinker, 11y, DSH, CatEHBDO

Oct JuneTotal protein 55 67 g/LAlbumin ↓20 - g/LGlobulin 35 - g/LAG ratio 0.6 -Sodium 157 154 mmol/LPotassium ↓3.5 4.3 mmol/LNa:K ratio ↑ 45 36Urea 4.7 11.1 mmol/LCreatinine 114 138 umol/LAlk Phos ↑ 324 89 U/LALT ↑ 1798 64 U/LTotal bilirubin ↑ 78 - umol/LBile acids ↑ 388.0 - umol/L

Evaluating renal function

Urea used as a sentinel molecule for nitrogenous waste in blood

Urea concentration is affected byRate of NH4 formation (protein breakdown)Rate of hepatic conversion to ureaRate of renal clearance Rate of intestinal excretion

Serum urea represents a composite of these factors

Evaluating renal function

Urea is more sensitive but less specific for renal function than creatinine

Hypovolaemia allows increased renal reabsorption of urea

Protein load from GI tract is variable GI bleeding may result in dogs in urea

increase unrelated to GFR

Causes of azotaemia

Prerenal causeshypovolaemia, shock, reduced cardiac output, hypoadrenocorticism

Renal causescongenital, inflammatory, toxic, renal ischaemia, neoplasia

Post renal causesurinary tract obstruction or leakage

Investigation of renal disease

Document persistence of the azotaemia Urinalysis

SG , dipstick, sediment (culture) Complete the profile

Urine Refactometer

Urinary Tract Infection In Cats

Increasingly common with age

Need not be associated with leuconuria

Leucocyte dipstick gives false positive

Reduced serum urea

Reduced protein intake Reduced protein absorbtion Reduced hepatic synthesis of urea Increased renal clearance of urea

Serum Electrolytes

Sodium Potassium Chloride

Hypokalaemia

Predominantly K+ is intracellular Serum K+ is insensitive for depletion of total

body potassium Most common in polyuric cats associated

with increased GFR Muscle weakness, anorexia, vomiting,

cardiac arrythmias

Tabatha, 16y, DSH,FNWeight loss, needs dental preOp checkTotal protein 66 g/L 54.0 - 80.0Albumin 26 g/L 21 - 39Globulin 40 g/L 15 - 57Sodium 147 mmol/L 125 - 160Potassium 3.3 mmol/L 3.6 - 6.0Na:K ratio 45 32 - 41Total calcium 2.28 mmol/L 2.0 - 3.0Urea 8.7 mmol/L 4.0 - 12.0Creatinine 111 umol/L 80 - 180Alk Phos ↑ 291 U/L 0 - 50ALT ↑ 136 U/L 0 - 40Total bilirubin 5 umol/L 0 - 10Glucose 15.5 mmol/L 3.5 - 6.6Total T4 ↑ 167.0 nmol/L 5.0 - 50.0

Hyperkalaemia

May accompany hypoaldosteronism in Addison’s disease

Affected by blood pH Increased in renal insufficiency and urinary

obstruction Occasionally seen with severe muscle

damage Cardiac conduction disturbances, depression,

weakness

Investigation of Electrolyte Abnormalities Exclude artefacts

preanalytical, analytical Check for underlying disease Correct pre-operatively

Hypercalcaemia

Closely controlled element involved in neuromuscular transmission

Minor deviations may be significant Present as free, protein bound and chelated

forms in blood Malignant neoplasia, parathyroid neoplasia,

Addisons, CRF

Preanaesthetic blood testing

Elective blood Testing

Sampling at consultation or vaccination Removes time pressure for medical decision

making Allows further testing if required ahead of

anaesthesia Increases flexibility of test procedures Improves client communication and

understanding

Elective blood Testing

Aims Screen for clinically occult disease where

early intervention is beneficial Provides baseline data Retained for future use To guide additional testing Facilitate improved perioperative

management

Elective blood testing

Test selection is based onHistory, signalment, physical findings

Screen or profile may be appropriateincorporate appropriate additional tests

Ensure pre-analytical & analytical error is minimised

Retain and compare data for an individual over time